Pumps can be classified into mechanical and non-mechanical varieties. Generally, the conventional mechanical pumps have issues with reliability of the moving pump-components. Electrokinetic pumps, on the other hand, contain no moving parts, making them suitable for a variety of applications, including fluid movement in microanalytical systems. EOPs are electrokinetic pumps, and provide a fluid flow due to movement of an electric double layer that forms at the solid-liquid interface. Application of an electric field across a porous membrane structure of an EOP results in a movement of the electric double layer, which results in a viscous drag. The viscous drag then causes a bulk fluid flow and generation of a net pressure.
Standard EOPs made from porous ceramic frit or packed capillaries require over 1 kV to establish the electric fields required for pumping. The electric field is generated using at least two electrodes disposed on either side of the porous membrane and an external power source. Generally, the current from the electrode is passed into the pumping solution via chemical reactions at the electrode surface, e.g. using a Pt electrode and water as the pumping solution to produce gases like hydrogen or oxygen, which may stall the pump. Alternative electrode materials are used in electrokinetic pumps, such as redox polymers, redox metal salts or oxides.
In addition to the alternative electrode materials, thin porous ceramic substrates have recently been employed to produce the highest pumping pressure per applied voltage due to high surface-to-volume ratios. The EOP for generating high pressure using low-voltage, external power source and thin EOP substrates, is recently being developed. In general, to increase the pumping pressure of low-voltage EOPs, increased surface area for electric double layer formation is required, however, increasing the thickness of the EOP substrate results in higher running voltages.
The alternate stacking arrangement of electrodes and membranes for a high pressure EOP solved the challenge of maintaining high electric field strengths using low running voltages. However, the need for self-containment of pumps and actuators in analytical, biomedical, pharmaceutical, environmental, and security monitoring applications has not been met. Therefore, the EOPs which are capable of generating high pressure using a lower applied voltage, without using an external power source, and with minimum membrane fabrication requirements, are desirable.